The Ariston Black Vent Cap Base for Flat Roof (Part No. 3318011) is the genuine Ariston weatherproofing flashing plate used when a vertical coaxial flue passes through a flat or low-pitch roof. It creates a fully watertight seal around the flue pipe penetration, preventing rainwater ingress at the roof surface — a critical detail on any vertical flue installation where the terminal exits through a flat roof rather than a pitched surface with a conventional angled flashing. Compatible with all Ariston HE condensing boilers using the standard Ø60/100 and Ø80/125 coaxial vertical flue systems, it pairs with the Vertical Starter (3318079) and the Vertical Flue Kit (3318080, 3318081, or 3319235) to complete a code-compliant vertical flue installation. Not included with any flue kit — this must be ordered separately whenever a flat-roof termination is required.
Ø60/100
Coaxial System — Standard HE
Ø80/125
Coaxial System — Extended
⚠ Must Be Fitted Before the Flue Terminal Is Installed: The vent cap base must be positioned and secured to the roof surface before the vertical flue terminal is pushed through and seated. Attempting to retrofit the flashing plate after the flue kit is in place is not possible without dismantling the flue assembly. Always plan the flashing installation sequence before committing to roof cuts.
⚠ For Flat Roofs Only — Not Suitable for Pitched Roofs: The 3318011 is designed for use on flat or near-flat roof surfaces (0–10° pitch). For pitched roofs, use the Ariston Flexible Base Cap Flashings — Part No. 3318009 (black, 12–40°) or 3318010 (red, 12–40°). Using a flat-roof base cap on a sloping surface will not create an adequate weatherproof seal and risks water ingress.
ℹ Note on 100mm Terminal Compatibility (3319235): The 3318011 is sized for the standard Ariston domestic 125mm terminal used by the 3318080 and 3318081 vertical flue kits. If you are installing the 3319235 leisure/caravan 100mm terminal, this flashing is unlikely to provide a correct seal around the smaller terminal — a 100mm-rated cowl or flashing specific to the leisure sector should be sourced instead.
Watertight Flat Roof Seal
The 3318011 is engineered to form a weatherproof seal at the point where the coaxial flue pipe passes through a flat roof. Without a properly fitted flashing, the annular gap between the pipe and the roof aperture provides a direct water ingress path — a latent defect that may not become apparent until the first significant rainfall after commissioning.
Genuine Ariston Part — Assured Compatibility
As a genuine Ariston accessory, the 3318011 is dimensioned and tested to work with Ariston's coaxial flue pipe outer diameter and terminal geometry. Third-party flat-roof flashings vary in internal aperture and sealing design — using a non-genuine flashing risks poor fitment and inadequate waterproofing, which would affect both Building Regulations compliance and warranty validity.
Dual Flue System Compatibility
The 3318011 is compatible with both the standard Ø60/100 coaxial system (used by E-Combi ONE, Clas ONE, Genus ONE, Alteas ONE) and the larger Ø80/125 coaxial system used on higher-output boilers or longer flue runs. This makes it a single stocking item suitable across most of the Ariston HE condensing range.
| Specifications — Ariston Black Vent Cap Base for Flat Roof |
| Part Number |
3318011 |
| Colour |
Black |
| Application |
Flat roof vertical flue termination weatherproofing |
| Suitable Roof Pitch |
Flat / near-flat (0–10°) |
| Compatible Flue Diameter |
Ø60/100 mm and Ø80/125 mm coaxial (125mm terminal — domestic kits) |
| Compatible Boiler Ranges |
All Ariston HE condensing boilers — E-Combi ONE, Clas ONE, Genus ONE, Alteas ONE, Alteas ONE+ NET and equivalent ranges |
| Used With |
Vertical Starter 3318079 + Vertical Flue Kit 3318080 (black) or 3318081 (red) |
| Not Compatible With |
3319235 leisure/caravan 100mm terminal — use a 100mm-rated leisure cowl instead |
| Alternative for Pitched Roofs |
3318009 (flexible base cap, black, 12–40°) / 3318010 (flexible base cap, red, 12–40°) |
| Included in Flue Kits |
No — must be ordered separately for all flat-roof vertical flue installations |
Frequently Asked Questions
Is the vent cap base included with the vertical flue kit?
No. Neither the standard Ariston vertical flue kits (3318080, 3318081) nor the leisure 100mm kit (3319235) include a roof flashing. The 3318011 must always be ordered separately for any flat-roof vertical flue installation. It is also not included with the Vertical Starter (3318079). Plan for this component at the quotation stage to avoid a delay during installation.
Can I use the 3318011 with the leisure 100mm flue kit (3319235)?
The 3318011 is sized for the 125mm terminal used on standard domestic Ariston vertical flue kits. The 3319235 uses a smaller 100mm terminal, so the 3318011 will not form a correct weatherproof seal around it. For leisure installations using the 3319235, source a 100mm cowl or flashing rated for that terminal diameter from a leisure/caravan heating specialist instead.
What is the installation sequence for a flat-roof vertical flue?
The correct sequence is: (1) fit and commission the boiler; (2) cut the 130mm diameter hole through the ceiling and roof; (3) fit and seal the 3318011 flashing plate to the roof surface with appropriate sealant for your roof membrane type; (4) fit the Vertical Starter (3318079) to the boiler manifold; (5) pass the vertical flue kit up through the ceiling and roof aperture; (6) push the flue kit into the starter and confirm all push-fit seals are fully engaged. Do not skip step 3 — the flashing must be in place before the terminal is seated through it.
What if my roof has a slight pitch — can I still use the 3318011?
The 3318011 is intended for flat or near-flat roof applications up to approximately 10°. Beyond that, the flat base plate will not sit flush against the roof surface and the seal will be compromised. For pitched roofs between 12° and 40°, use the Ariston flexible base cap flashing — Part No. 3318009 (black) or 3318010 (red), which conform to the roof surface across that pitch range.
